This research is concerned primarily with nucleic acid metabolism in mammalian cells featuring studies on the biogenesis of messenger RNA. Growing cells not transformed by viruses as well as cells transformed by and infected by tumor viruses are being studied with the major effort devoted to the details involved in the transcription and conversion of large nuclear RNA molecules into functional polysomal messenger RNA. The long range goal is to understand the regulation of mRNA production in mammalian cells since this must be a pivotal point of regulation in cell growth. BIBLIOGRAPHIC REFERENCES: Sheiness, D., Puckett, L. and Darnell, J.E. (1975). Possible Relationship of Poly(A) Shortening to mRNA Turnover. Proc. Nat'l. Acad. Sci. USA 72, 1977. Hoffmann, P.R. and Darnell, J.E. (1975). Differential Accumulation of Virus-Specific RNA During the Cell Cycle of Adenovirus-Transformed Rat Embryo Cells. Jrnl. of Virol. 16, 806.